Effect Of Nitrogen On Characteristics Of Growth Of Pinus Tabulaeformis Seedlings

To explore the relation of root order and diameter and the nitrogen fertilization effect on the growth characteristics of Pinus tabulaeformis, the 2 year old Pinus tabulaeformis seedlings were treated with 5 nitrogen levels in continuous 3-year (nitrogen application rate were 0.02, 0.04, 0.08, 0.16 and 0.32g/kg). And the effect of increased soil available nitrogen on the aboveground and root characteristics were investigated. Also the respective advantages of the root order and diameter classes in root morphology characteristics description were discussed. And the relationship between these two classification methods was attempted to reach. The main conclusions were as follows:1. The impacts of nitrogen fertilization on aboveground characteristics of Pinus tabulaeformis seedlings were as follows: (1) With the increasing concentration of soil available nitrogen, the leaf area, leaf biomass and specific leaf area increased in the first place and then decreased, but the differences were not significant (P>0.05). The branch biomass of 0.04g/kg nitrogen level increased significantly, while that of 0.16 and 0.32g/kg level reduced significantly. (2) The net photosynthetic rate (Pn) of 3 year old Pinus tabulaeformis seedlings increased significantly at 0.08g/kg level. And there were no significant difference in other tratments. That indicated that 0.08g/kg treatment could effectively improve the seedlings photosynthetic capacity of Pinus tabulaeformis. The path analysis showed that the photosynthetic active radiation (PAR), stomatal conductance (Cond), intercellular CO2 concentration (Ci) and transpiration rate (Tr) were important factors that influenced net Pn.2. The impacts of nitrogen fertilization on root characteristics were as follows: (1)Nitrogen fertilization reflected on the significant decrease of root diameter, root area and specific root area in root orders I and II. High concentrations of nitrogen can significantly reduce root length in root orders I and II. (2) The effect of nitrogen fertilization on root biomass and specific root length were not significant.3. At the individual level, the result of total biomass showed that the biomass of roots and leaves reduced significantly under high concentration of nitrogen . In the whole plant, the biomass reduced significantly under treatment 0.32g/kg. And there were no significant changes of seedling biomass under low nitrogen treatment (0.02-0.08g/kg). Combining with the photosynthetic characterstics result, 0.08g/kg was the most suitable nitrogen level for the growth of Pinus tabulaeformis seedlings.4. The relationship analysis of the root diameter and four species root orders indicated that diameter ranges can be divided according to the diameter of the root orders. And it can reflect root orders through logical division of the root diameter classes. A new diameter classification was proposed:≤0.4, 0.4–0.8, 0.8–1.1, 1.1-1.3 and 1.3–2.0 mm, based on the principle that diameter maximum ratio could reflect root orders. These intervals could represent 55% of root tip, 61% of root length and 60% of root area in I, II, III, IV and V root order. This method was also suitable to the determination of Pinus bungeana Zucc, Pinus sylvestrisvar.mongolica and Pinus armandii diameter ranges. It could rise diameter classification accuracy (such as by 0.5, 1.0, 1.5 and 2.0mm) and overcome the difficulty of applying the root order classification method in root defects screening. Thus, this method can effectively improve the root order of the sampling procedures and the accuracy and efficiency of statistic.